Semiconductor laser device and manufacturing method thereof

ABSTRACT

A semiconductor laser device includes a chip obtained from a substrate and a semiconductor multi-layer formed on the substrate. The semiconductor multi-layer is formed from a plurality of semiconductor layers of a semiconductor material having a hexagonal structure, and includes a stripe-shaped wave guide portion. The chip includes two chip end facets that extend in a direction crossing an extending direction of the wave guide portion. Each of regions on both sides of the wave guide portion in at least one of the chip end facets has a notch portion formed by notching a part of the chip, and the notch portion exposes a first wall surface connecting to the chip end facet and a second wall surface connecting to the chip side facet. An angle between an extending direction of the first wall surface in at least one of the two notch portions and an extending direction of the cleavage facet is in a range of about 10 degrees to about 40 degrees.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 on PatentApplication No. 2006-238086 filed in Japan on Sep. 1, 2006, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a semiconductor laser device and amanufacturing method thereof. More particularly, the invention relatesto a semiconductor laser device having a chip end facet formed bycleavage, and a manufacturing method thereof.

2. Background Art

III-V compound semiconductor laser devices such as aluminum galliumarsenic (AlGaAs)-based infrared laser devices or indium galliumphosphorus (InGaP)-based red laser devices have been widely used aselements of communication devices or as reading and writing elements ofCDs (Compact Discs) or DVDs (Digital Versatile Discs). Recently, blue orultraviolet semiconductor laser devices having a shorter wavelength havebeen implemented by using a nitride semiconductor represented by generalformula Al_(x)Ga_(y)In_((1-x-y))N (where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1).Semiconductor laser devices using a nitride semiconductor have beengradually used in practical applications as reading and writing lightsources of next generation high-density optical discs such as Blu-rayDisc. Blue laser devices of several tens of milliwatts are currentlyavailable on the market. However, higher output has been demanded for animproved recording speed, and 100 m W-level laser devices are comingonto the market.

In a semiconductor laser device, a resonator end facet is generallyformed by cleavage. In infrared and red semiconductor laser devices thatare formed from a semiconductor material having a Zinc-blende structure,such as AlGaAs-based and GaInP-based semiconductor materials, thesemiconductor has a cleavage facet at every 90 degrees and therefore hasvery high cleavage accuracy. However, since a crystal structure of anitride semiconductor such as GaN is a hexagonal wurtzite structure, thesemiconductor has a (1-100) face as a cleavage facet and an equivalentcleavage facet that is 60 degrees away from the (1-100) face. Therefore,upon cleavage, cracks are formed also in the direction of 60 degreesfrom the cleavage direction, and it is difficult to form a structurallystable cleavage facet.

In order to solve this problem, Japanese Patent Laid-Open PublicationNo. 2003-17791 discloses a method for forming a scribe mark like adashed line on a nitride semiconductor layer by using a diamond needleor the like, and conducting cleavage by breaking by using the scribemark as a cleavage guide. However, when cleavage guide grooves areformed by scribing or dicing, a nitride semiconductor layer isscratched. Therefore, a lot of defects such as end facet cracks,unevenness, fractures, and chips are generated in the groovesthemselves, causing a cleavage facet to be displaced. Moreover, sincegrooves formed by scribing do not necessarily have a uniform shape, itis difficult to accurately control the cleavage position.

Japanese Patent No. 59-14914 and Japanese Patent Laid-Open PublicationNo. 11-251265 disclose a method for forming cleavage guide grooves byetching. When cleavage guide grooves are formed by etching, the positionand shape of the grooves can be accurately controlled.

However, the inventors found that, in the case of a nitridesemiconductor, an intended cleavage facet still cannot be obtained evenwhen the cleavage guide grooves are formed. More specifically, asdescribed above, a nitride semiconductor essentially has a poor cleavageproperty, and has an equivalent cleavage facet in the direction of 60degrees from a cleavage facet. Therefore, even when cleavage guidegrooves are formed, cleavage does not occur along the grooves, orcleavage starts from a portion other than the end of the groove.Accordingly, an intended cleavage facet cannot be obtained.

SUMMARY OF THE INVENTION

The invention is made in order to solve the conventional problems, andit is an object of the invention to implement a semiconductor laserdevice using a semiconductor material of a hexagonal system such as anitride semiconductor and having a structurally stable cleavage facet,and a manufacturing method of such a semiconductor laser device.

In order to achieve the above object, in a semiconductor laser device ofthe invention, a cleavage guide has an end portion having a V shape whenviewed two dimensionally.

More specifically, a semiconductor laser device according to one aspectof the invention includes a chip obtained from a substrate and asemiconductor multi-layer formed on the substrate. The semiconductormulti-layer is formed from a plurality of semiconductor layers of asemiconductor material having a hexagonal structure, and includes astripe-shaped wave guide portion. The chip includes two chip end facetsthat extend in a direction crossing an extending direction of the waveguide portion, and two chip side facets that extend in parallel with theextending direction of the wave guide portion. A region including thewave guide portion in each chip end facet is a cleavage facet resultingfrom cleavage of the semiconductor multi-layer. Each of regions on bothsides of the wave guide portion in at least one of the chip end facetshas a notch portion formed by notching a part of the chip. The notchportion exposes a first wall surface connecting to the chip end facetand a second wall surface connecting to the chip side facet. An anglebetween an extending direction of the first wall surface in at least oneof the two notch portions and an extending direction of the cleavagefacet is in a range of about 10 degrees to about 40 degrees.

In the semiconductor laser device of the invention, the extendingdirection of the first wall that serves as a cleavage guide issignificantly different from that of a crystal face that is equivalentto the cleavage facet. Accordingly, cleavage is less likely to proceedin a direction different from the extending direction of the cleavagefacet, whereby an accurate cleavage facet can be formed. As a result, asemiconductor laser device having a structurally stable cleavage facetis implemented.

A method for manufacturing a semiconductor laser device according toanother aspect of the invention includes the steps of: (a) forming asemiconductor wafer that has a plurality of stripe-shaped wave guideportions extending in one direction at intervals by first forming on asubstrate a semiconductor multi-layer including an n-type clad layer, anactive layer, and a p-type clad layer and then selectively etching thep-type clad layer; (b) selectively etching the semiconductor waferhaving the plurality of wave guide portions to form a plurality ofgrooves arranged in a line in a region except for the wave guideportions in a direction crossing an extending direction of the waveguide portions; and (c) by using the plurality of grooves arranged in aline as a cleavage guide, forming a cleavage facet exposing the waveguide portions along the cleavage guide. Each groove has an end portionat at least one of its two ends located in a direction crossing anextending direction of the wave guide portions, and the end portion hasa V shape when viewed two dimensionally. An angle between two sidessurrounding the end portion is in a range of about 20 degrees to about80 degrees, and an angle between an extending direction of at least oneof the two sides surrounding the end portion and a direction in whichthe cleavage facet is formed is in a range of about 10 degrees to about40 degrees.

In the method for manufacturing a semiconductor laser device accordingto the invention, the direction of the end portions of the grooves thatserve as a cleavage guide is significantly different from the extendingdirection of a crystal face that is equivalent to the cleavage facet.Accordingly, cleavage is less likely to proceed in a direction otherthan the extending direction of the cleavage facet, whereby cleavage canbe accurately conducted along a cleavage line connecting the endportions of the grooves. As a result, a semiconductor laser device canbe manufactured with an excellent yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C show a semiconductor laser device according to afirst embodiment of the invention, wherein FIG. 1A is a perspectiveview, FIG. 1B is a plan view, and FIG. 1C is a cross-sectional view onthe side of a chip end facet;

FIGS. 2A, 2B, and 2C show a semiconductor wafer for manufacturing asemiconductor laser device according to the first embodiment of theinvention, wherein FIG. 2A is a plan view, FIG. 2B is a cross-sectionalview taken along line IIb-IIb in FIG. 2A, and FIG. 2C is across-sectional view taken along line IIc-IIc in FIG. 2A;

FIGS. 3A and 3B show a cleavage facet of the semiconductor laser deviceof the first embodiment of the invention, wherein FIG. 3A is a plan viewand FIG. 3B is a cross-sectional view;

FIGS. 4A, 4B, and 4C are plan views showing a relation between an angleof an end portion of a groove and a cleavage line in the semiconductorlaser device of the first embodiment of the invention;

FIG. 5 is a graph showing a correlation between an angle of an endportion of a groove and a functioning ratio of a cleavage guide in thesemiconductor laser device of the first embodiment of the invention;

FIG. 6 is a graph showing a correlation between a width of a groove anda functioning ratio of a cleavage guide in the semiconductor laserdevice of the first embodiment of the invention;

FIG. 7 is a graph showing a correlation between a depth of a groove anda functioning ratio of a cleavage guide in the semiconductor laserdevice of the first embodiment of the invention;

FIG. 8 is a perspective view showing a modification of the semiconductorlaser device of the first embodiment of the invention;

FIGS. 9A and 9B show a cleavage facet in a modification of thesemiconductor laser device of the first embodiment of the invention,wherein FIG. 9A is a plan view and FIG. 9B is a cross-sectional view.

FIGS. 10A and 10B show a cleavage facet in a modification of thesemiconductor laser device of the first embodiment of the invention,wherein FIG. 10A is a plan view and

FIG. 10B is a cross-sectional view;

FIGS. 11A and 11B show a cleavage facet in a modification of thesemiconductor laser device of the first embodiment of the invention,wherein FIG. 11A is a plan view and FIG. 11B is a cross-sectional view;

FIG. 12 is a perspective view of a semiconductor laser device accordingto a second embodiment of the invention;

FIGS. 13A and 13B show a cleavage facet of the semiconductor laserdevice according to the second embodiment of the invention, wherein FIG.13A is a plan view and FIG. 13B is a cross-sectional view;

FIGS. 14A and 14B show a cleavage facet in a modification of thesemiconductor laser device of the second embodiment of the invention,wherein FIG. 14A is a plan view and FIG. 14B is a cross-sectional view;

FIGS. 15A and 15B show a cleavage facet of a semiconductor laser deviceaccording to a third embodiment of the invention, wherein FIG. 15A is aplan view and FIG. 15B is a cross-sectional view; and

FIGS. 16A and 16B show a cleavage facet of a semiconductor laser deviceaccording to a fourth embodiment of the invention, wherein FIG. 16A is aplan view and FIG. 16B is a cross-sectional view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinafter, a first embodiment of the invention will be described withreference to the drawings. FIGS. 1A through 1C show the structure of asemiconductor laser device according to the first embodiment. FIG. 1Ashows the whole structure of the semiconductor laser device, FIG. 1Bshows a planar structure of the semiconductor laser device, and FIG. 1Cshows a cross-sectional structure on the side of a resonator end facet.The semiconductor laser device of this embodiment is a semiconductorchip obtained from a semiconductor wafer with multi-layer of nitridesemiconductors.

As shown in FIGS. 1A through 1C, the semiconductor laser of thisembodiment includes a substrate 11 formed from gallium nitride (GaN),and a nitride semiconductor multi-layer 12 formed on the substrate 11.The nitride semiconductor multi-layer 12 has an n-type semiconductorlayer 21, an active layer 22, and a p-type semiconductor layer 23 whichare sequentially epitaxial-grown on the substrate 11. The active layer22 is formed from InGaN and has a multiple quantum well structure. Aridge stripe portion 23 a is formed by selectively etching the p-typesemiconductor layer 23.

A dielectric layer 24 for confining a current is formed on the p-typesemiconductor layer 23 except on the top of the ridge stripe portion 23a. On the dielectric layer 24 is formed a p-side electrode 25 in contactwith the top of the ridge stripe portion 23 a. An n-side electrode 26 isformed on the rear surface of the substrate 11, that is, on the surfaceof the substrate 11 which is located on the opposite side of the nitridesemiconductor multi-layer 12.

In the semiconductor laser device of this embodiment, a chip end facet13 that extends approximately perpendicular to the extending directionof the ridge stripe portion 23 a is formed by cleaving a semiconductorwafer. On the other hand, a chip side facet 14 that extendsapproximately parallel to the extending direction of the ridge stripeportion 23 a is formed by dicing the semiconductor wafer. In thisembodiment, a central part of the chip end facet 13 which includes theridge stripe portion 23 a is a smooth cleavage facet 13 a, that is, anexposed (1-100) face of the nitride semiconductor multi-layer 12. Theregions of the chip end facet 13 which are located on both sides of thecleavage facet 13 a are formed by cleavage. However, these regions arenot a perfect cleavage facet and have cleavage cracks, steps, and thelike. Hereinafter, a “cleavage facet” does not refer to a facet that isformed by cleavage, but refers to a single crystal face exposed bycleavage.

When the semiconductor laser device of this embodiment is seen from theside of the chip end facet 13, a notch portion 31 is formed on bothsides of the cleavage facet 13 a. The notch portions 31 are formed bynotching a part of the nitride semiconductor multi-layer 12. The planarshape of the notch portion 31 is approximately a right-angled trapezoid.The notch portion 31 exposes a first wall surface 31 a connecting to thechip end facet 13 and a second wall surface 31 b connecting to the chipside facet 14. An angle θ between the extending direction of the firstwall surface 31 a and the extending direction of the cleavage facet 13 ais in the range of 10 degrees to 40 degrees. Details of the notchportion 31 will be given later.

FIGS. 2A through 2C show the structure of a pre-cleavage semiconductorwafer for forming a semiconductor laser device according to the firstembodiment. FIG. 2A shows a planar structure of the semiconductor wafer,FIG. 2B shows a cross-sectional structure of the semiconductor wafertaken along line IIb-IIb, and FIG. 2C shows a cross-sectional structureof the semiconductor wafer taken along line IIc-IIc.

As shown in FIGS. 2A through 2C, a semiconductor wafer 10 of the firstembodiment includes a substrate 11 and a nitride semiconductormulti-layer 12. The nitride semiconductor multi-layer 12 has a pluralityof ridge stripe portions 23 a formed on a (0001) face of the substrate11. The plurality of ridge stripe portions 23 a extend along a <1-100>orientation of the substrate 11 and are spaced apart from each other.The nitride semiconductor multi-layer 12 has a plurality of grooves 32formed by etching the nitride semiconductor multi-layer 12 except theridge stripe portions 23 a. These grooves 32 are arranged in a linealong a <11-20> orientation of the substrate 11. A plurality of cleavageguide grooves 33 are thus formed spaced apart from each other. Chips 41of the semiconductor laser device are obtained as follows: the nitridesemiconductor multi-layer 12 is first cleaved along each cleavage guidegroove 33 to form a chip end facet 13. The semiconductor wafer is thendivided into chips 41 by dicing in the direction parallel to theextending direction of the ridge stripe portions 23 a. Approximately aquarter of each groove 32 remains in each chip 41, forming a notchportion 31.

Each groove 32 is formed by dry etching the nitride semiconductormulti-layer 12, and both ends of the groove 32 are V-shaped when viewedtwo dimensionally. When the grooves 32 are formed by dry etching, theposition and shape of the grooves 32 can be accurately controlled, asopposed to the case where guide grooves are formed by scribing.Therefore, the grooves 32 can be shaped so as to function as a cleavageguide to the maximum extent possible, whereby cleavage yield can besignificantly improved.

When viewed two dimensionally, each groove 32 has a flat hexagonal shapehaving sharp ends along the direction crossing the ridge stripe portions23 a. Therefore, cleavage is likely to occur along the line connectingthe tips of the grooves 32, whereby a cleavage facet of an intendedorientation can be easily formed.

Hereinafter, the shape of the grooves 32 will be described in furtherdetail. FIGS. 3A and 3B show the structure of a portion between thegrooves 32 when the semiconductor wafer 10 is cleaved. FIG. 3A shows aplanar structure, and FIG. 3B shows a cross-sectional structure. Eachgroove 32 is divided into halves by cleavage, forming notch portions 31.The state before the groove 32 is divided into halves will now bedescribed.

In the case of a nitride semiconductor having a hexagonal crystalstructure, it is difficult to accurately form a cleavage line along acleavage guide even when a cleavage guide is formed by grooves arrangedin a line and having a rectangular planar shape. In this embodiment,each groove 32 has a base portion 32 a and end portions 32 b located onboth sides of the base portion 32 a, and the base portion 32 a isrectangular and each end portion 32 b has a V-shape when viewed twodimensionally. In other words, each groove 32 has sharp ends along thedirection crossing the ridge stripe portions 23 a. Accordingly, evenwhen a cleavage line 51 is displaced, the direction of the cleavage lineis corrected along the wall surface of the end portion 32 b, andcleavage is conducted from the tips of the groove 32 as shown in FIG.3A. As a result, an accurate cleavage line can be formed in a regionincluding the ridge strips portion 23 a.

The direction of the cleavage line 51 is corrected by the wall surfaceof the end portion 32 b due to cleavage cracks and steps that areproduced in a region where the cleavage line 51 and the wall surface ofthe end portion 32 b cross each other. Since fine cleavage cracks andthe like are formed along the wall surface of the end portion 32 b, thecleavage line 51 is guided in the direction along the wall surface ofthe end portion 32 b. Accordingly, an angle at which the wall surface ofthe end portion 32 b and the cleavage line 51, a cleavage facet, crosseach other is very important.

FIGS. 4A through 4C schematically show the cleavage results for variousgrooves 32 having different angles 20 between the wall surfaces of theend portion. The grooves 32 are formed in the nitride semiconductormulti-layer 12 formed on the GaN substrate 11.

In FIG. 4B, the angle 20 at the tip of each groove 32 is 60 degrees. Inthis case, even when the cleavage line 51 is displaced in the baseportion 32 a of the groove 32, the direction of the cleavage line 51 iscorrected along the wall surface of the end portion 32 b. As a result,the cleavage line 51 connecting the respective tips of the grooves 32can be obtained. In FIGS. 4A and 4C, on the other hand, the angle 20 atthe tip of each groove 32 is 20 degrees or less, or 80 degrees or more.In this case, there is almost no effect of correcting the direction ofthe cleavage line 51 in the end portion 32 b.

FIG. 5 shows a correlation between the angle 2θ at the tip of eachgroove 32 and the functioning ratio of the cleavage guide. Thefunctioning ratio of the cleavage guide herein indicates the ratio thatthe cleavage line connecting the respective tips of the grooves 32 wasobtained. FIG. 5 shows a normalized functioning ratio, wherein thefunctioning ratio is 1 when the angle 2θ at the tip of the groove 32 isabout 60 degrees. Whether the cleavage line connecting the respectivetips of the grooves 32 was obtained or not was determined by microscopicobservation. In this example, about 100 samples were observed. It shouldbe noted that, in this observation, each groove 32 had a width w of 20μm and a depth t of 2 μm, and a distance d between the tips of thegrooves 32 was 50 μm. The width w, the depth t, and the distance d areas shown in FIGS. 3A and 3B.

As shown in FIG. 5, when the angle 2θ at the tip of the groove 32 ismore than 80 degrees or less than 20 degrees, the normalized functioningratio of the cleavage guide is 0.5 or less. This shows that the grooves32 do not sufficiently function as a cleavage guide. This is aphenomenon specific to a nitride semiconductor having a hexagonalcrystal structure. Since a nitride semiconductor has a hexagonalwurtzite structure, it has a facet equivalent to a face of <1-100>orientation, that is, a facet equivalent to a cleavage facet, at every60 degrees. When the angle 2θ at the tip of each groove 32 is 60degrees, the angle θ between the central axis of the groove 32 which isparallel to <11-20> orientation and each wall surface of the end portion32 b is 30 degrees. In this case, the wall surface of the end portion 32b extends in the direction farthest from the cleavage facet.

Accordingly, the angle 2θ at the tip of the groove 32 is preferablydetermined such that the wall surface of the end portion 32 b extends inthe direction as far away from the cleavage facet and a facet equivalentto the cleavage facet as possible. More specifically, the angle 2θ is inthe range of 20 degrees and 80 degrees. Preferably, the angle 2θ is inthe range of 40 degrees and 70 degrees in which the functioning ratio ofthe cleavage guide is 0.9 or more. More preferably, the angle 2θ is 60degrees. The angle θ between the extending direction of the wall surfaceof the end portion 32 b and the extending direction of the cleavagefacet is half of the angle 2θ, that is, in the range of 10 degrees and40 degrees.

The result of studying the width w of the groove 32 will now bedescribed. When the cleavage line 51 is formed within the groove 32, thewidth w of the groove 32 hardly affects the function to correctdisplacement of the cleavage line. However, it was found that when thewidth w of the groove 32 is 10 μm or less, the cleavage line 51 maydeviate from the groove 32 due to fine defects, foreign matter or thelike. If the cleavage line 51 deviates to the outside of the groove 32,the cleavage line 51 cannot go back to the inside of the groove 32 andthe groove 32 loses its function as a cleavage guide. As a result, mostof the chips 41 formed in a line will have defective cleavage.

FIG. 6 shows a correlation between the width w of the groove 32 and thefunctioning ratio of the cleavage guide. FIG. 6 shows a normalizedfunctioning ratio, wherein the functioning ratio of a cleavage guidewith the groove 32 having a width w of 20 μm is 1. In this example, theangle 2θ at the tip of the groove 32 is about 60 degrees, the depth t ofthe groove 32 is 2 μm, and the distance d between the respective tips ofthe grooves 32 is 50 μm.

FIG. 6 shows that the function of the cleavage guide degrades when thewidth w of the cleavage guide is 10 μm or less. This is because thecleavage line is likely to deviate to the outside of the groove 32 whenthe width w is 10 μm or less. On the other hand, when the width w of thegroove 32 is too large, gold plating or the like for wiring cannot beformed in the groove 32. Therefore, heat dissipation property of the endfacet portion degrades, causing degradation in element characteristics.Accordingly, it is practically desirable that the width w of the groove32 be 50 μm or less.

The result of studying the effect of the distance d between therespective tips of the grooves 32 on the function as a cleavage guidegroove will now be described. In this example, the grooves 32 wereformed at various intervals in the nitride semiconductor multi-layer 12formed on the GaN substrate 11, and cleavage was conducted. It was foundthat a cleavage line is likely to be displaced between the grooves 32when the distance d between the tips of the grooves 32 is 100 μm ormore.

FIG. 7 shows a correlation between the distance d between the respectivetips of the grooves 32 and the functioning ratio of the cleavage guide.FIG. 7 shows a normalized functioning ratio, wherein the functioningratio of the cleavage guide is 1 when the distance d is 20 μm. As shownin FIG. 7, the functioning ratio of the cleavage guide reduces as thedistance d increases. To be exact, the extending direction of thegrooves 32 does not match the extending direction of a (1-100) crystalface, a cleavage facet, and there is a slight difference in anglebetween the extending direction of the grooves 32 and the extendingdirection of the (1-100) crystal face. Therefore, as the distancebetween the grooves 32 increases, cleavage cracks are more likely to beproduced between the grooves, reducing the functioning ratio of thecleavage guide. Accordingly, the distance d between the grooves 32should be 100 μm or less, and preferably, is 40 μm or less. When thedistance d between the grooves 32 is too small, the tip of each groove32 gets too close to a corresponding ridge stripe portion 23 a, andcleavage cracks formed at the end portion of the groove 32 may affectlaser characteristics. Accordingly, the distance d between the grooves32 is preferably 20 μm or more.

The result of studying the depth t of the groove 32 will now bedescribed. The function of the cleavage guide was examined for thegrooves 32 having different depths t. When the depth t was less than 1μm, the function of the cleavage guide degraded significantly. However,when the depth t was 1 μm or more, the groove 32 sufficiently functionedas a cleavage guide. Moreover, the larger the depth t of the groove 32was, the more the function of the cleavage guide improved. However, whenthe groove 32 having a depth t of 10 μm or more is formed by dryetching, a mask material needs to be thick. This is because there isalmost no mask material having a large selectivity to GaN. As thethickness of the mask material is increased, pattern resolution andaccuracy are degraded, whereby the tips of the resultant grooves 32 getblunt. As a result, the cleavage position cannot be preciselycontrolled. Accordingly, the depth t of the groove 32 should be in therange of 1 μm and 10 μm, and preferably, in the range of 2 μm and 5 μm.

The thickness of the nitride semiconductor multi-layer 12 of thisembodiment is about 4 μm. The depth t of the groove 32 may be largerthan the thickness of the nitride semiconductor multi-layer 12 and thestructure as shown in FIG. 8 may be formed. Cleavage yield can beimproved by this structure. The reason for this is considered asfollows: the bottom of the end portion of the guide groove is subjectedto the largest stress. Therefore, in this structure, the largest stressis applied not to the inside of the nitride semiconductor multi-layer 12but to the inside of the substrate 11. Accordingly, excessive stress canbe prevented from being applied to the nitride semiconductor multi-layer12 upon cleavage.

When dry etching is used to form the groove 32, the shape of the bottomof the groove 32 can be changed depending on conditions of dry etchingsuch as power, pressure, and gas species. As shown in FIGS. 9A and 9B,when the groove 32 is deeper in the end portion 32 b than in the baseportion 32 a, cleavage cracks and steps are generated intensively at thetip of the groove 32 upon cleavage. Therefore, an excellent cleavagefacet 13 a can be formed in a region including the ridge stripe portion23 a, whereby yield is improved. The reason for this is considered asfollows: since the tip of the groove 32 has a sharp angle at the bottom,stress is applied intensively to the tip of the groove 32, wherebycleavage cracks and the like are likely to be generated. By thuscontrolling cleavage cracks and steps to be generated at a specificposition, defective cleavage in the ridge stripe portion 23 a, astripe-shaped wave guide portion, is suppressed and yield can beimproved.

In this embodiment, the groove 32 has a base portion 32 a and an endportion 32 b on both sides of the base portion 32 a. The base portion 32a has a rectangular shape and each end portion 32 b has a V shape whenviewed two dimensionally. As shown in FIGS. 10A and 10B, however, thegroove 32 may alternatively have an end portion 32 b at only one end ofthe base portion 32 a. When each groove 32 has an end portion 32 b onboth sides of the base portion 32 a and the grooves 32 are arranged sothat the respective tips of adjacent two grooves 32 facet each other, acleavage line connecting the two tips is likely to be fowled. Therefore,the position of the cleavage line can be accurately controlled. However,when the tips facing each other are misaligned, the cleavage line doesnot match the crystal face, causing cracks to be generated. Therefore,by forming the grooves 32 having an end portion 32 b only on one side ofthe base portion 32 a and arranging the grooves 32 so that the tip ofthe groove 32 facets the base portion 32 a of an adjacent groove 32,generation of cracks resulting from misalignment of the tips of thegrooves 32 can be suppressed. Alternatively, a groove 32 having a baseportion 32 a and an end portion 32 b on both sides of the base portion32 a and a groove 32 having only a base portion 32 a may be arrangedalternately.

In this embodiment, the end portion 32 b of the groove 32 has a V shapewhen viewed two dimensionally, and two sides of the end portion 32 bhave the same length. As shown in FIGS. 11A and 11B, however, the groove32 may alternatively be shaped such that the end portion 32 b isnarrowed only from one side. In this case, the end portion 32 b of eachgroove 32 has only one side that guides a cleavage line. Accordingly,the angle at the tip of the groove 32 is θ rather than 2θ.

Hereinafter, an example of a method for manufacturing a semiconductorlaser device according to the first embodiment will be described. First,an n-GaN buffer layer (not shown) of 200 nm thickness is grown on ann-type GaN substrate 11 having a carrier concentration of about 10¹⁸cm⁻³ by a metal organic chemical vapor deposition (MOCVD) method. Ann-type semiconductor layer 21, an active layer 22 having a triplequantum well structure, and a p-type semiconductor layer 23 are thensuccessively formed. The n-type semiconductor layer 21 includes an n-GaNlayer of 1 μm thickness, an n-Al_(0.04)Ga_(0.96)N clad layer of 1.8 μmthickness, and an n-GaN optical guide layer of 150 nm thickness. Theactive layer 22 includes an In_(0.10)Ga_(0.90)N well layer of 3 nmthickness and an In_(0.02)Ga_(0.98)N barrier layer of 7.5 nm thickness.The p-type semiconductor layer 23 includes a p-GaN optical guide layerof 120 μm thickness, a p-Al_(0.05)Ga_(0.95)N clad layer of 0.5 μmthickness, and a p-GaN contact layer of 100 nm thickness. The n-typesemiconductor layer 21 is doped with silicon (Si) at about 5×10¹⁷ cm⁻³as donor impurities, and the p-type semiconductor layer 23 is doped withmagnesium (Mg) at about 1×10¹⁹ cm⁻³ as acceptor impurities. Thep-contact layer, the uppermost layer of the p-type semiconductor layer23, is highly doped with Mg at about 1×10²⁰ cm⁻³. It should be notedthat the semiconductor multi-layer structure of this embodiment is byway of example only, and the semiconductor lamination structure and thegrowth method are not limited to those described above.

Thereafter, a silicon oxide (SiO₂) film of 20 nm thickness is depositedon the p-type contact layer by an CVD (chemical vapor deposition)method. Heat treatment of 800° C. is conducted in an N₂ atmosphere for30 minutes to activate Mg in the p-type semiconductor layer 23. Astripe-shaped SiO₂ mask is then formed by photolithography and dryetching using reactive ion etching (RIE). By using the SiO₂ mask, dryetching is conducted using inductively coupled plasma (ICP) with Cl₂gas, whereby the p-type semiconductor layer 23 is etched to about 0.5 μmthickness and a ridge stripe portion 23 a is formed. Heat treatment of800° C. is then conducted in an N₂ atmosphere for 30 minutes in order torecover damages caused by the ICP dry etching. The SiO₂ film used as amask is removed by buffer hydrofluoric acid (BHF), and a SiO₂ film of200 nm thickness is then deposited as a SiO₂ dielectric layer 24.

An opening that exposes only the top of the ridge stripe portion 23 a isformed in the SiO₂ dielectric layer 24 by photolithography and wetetching using a buffered hydrofluoric acid (BHF) solution. A p-sideelectrode 25 is then formed by photolithography and electron-beamdeposition. The p-side electrode 25 is formed from palladium (Pd) andplatinum (Pt). The thicknesses of Pd and Pt are 40 nm and 35 nm,respectively, and the deposition is conducted with the substrate heatedat 70° C. Thereafter, heat treatment of 400° C. is conducted, wherebyexcellent contact resistance of 5×10⁻⁴ Ωcm² or less is obtained. Ourstudy shows that the best contact resistance is obtained when thedeposition is conducted at about 70° C. to about 100° C. Given the heatresistance of a resist used for patterning, deposition at 70° C. is anoptimal condition that does not reduce the process yield and thatimproves the contact resistance.

By photolithography and ICP dry etching, grooves 32 are formed on eachline forming a chip end facet, whereby cleavage guide grooves 33 areformed like a dashed line as shown in FIGS. 2A through 2C. Note that, asshown in FIGS. 3A and 3B, the grooves 32 are not formed in the ridgestripe portions 23 a. After gold electrode pad for wiring is formed onthe p-side electrode 25, the rear surface of the substrate 11 is groundand polished so that the substrate 11 has a thickness of about 100 μm.An n-side electrode 26 is then formed on the rear surface of thesubstrate 11. The n-side electrode 26 is formed from titanium (Ti),platinum (Pt), and gold (Au), and the thicknesses of Ti, Pt, and Au are5 nm, 100 nm, and 500 nm, respectively. Excellent contact resistance onthe order of 10 ⁴ Ωcm⁻² or less can thus be implemented.

Finally, cleavage is conducted by breaking the substrate 11 from therear surface along the cleavage guide grooves 33, whereby chip endfacets are formed. Moreover, chips are cut out in parallel with theridge stripe portion 23 a by dicing. Semiconductor laser devices arethus obtained.

Second Embodiment

Hereinafter, a second embodiment of the invention will be described withreference to the drawings. FIG. 12 shows a semiconductor laser deviceaccording to a second embodiment of the invention. In FIG. 12, the sameelements as those of FIGS. 1A through 1C are denoted with the samereference numerals and characters, and description thereof will beomitted.

As shown in FIG. 12, in the semiconductor laser device of thisembodiment, a p-type semiconductor layer 23, an active layer 22, and apart of an n-type semiconductor layer 21 are etched on both sides of aridge stripe portion 23 a so that a mesa-shaped stepped portion 35 isformed for element isolation.

In this embodiment, the mesa-shaped stepped portion 35 is formed betweeneach groove 32 and the ridge stripe portion 23 a in the directionparallel to the extending direction of the ridge stripe portion 23 a.Forming such a stepped portion 35 can suppress generation of cleavagecracks and the like in a cleavage facet 13 a.

Hereinafter, the reason why forming the stepped portion 35 can suppressgeneration of cleavage cracks will be described. FIGS. 13A and 13B showthe structure of a portion between grooves 32 of the semiconductor laserdevice of this embodiment. FIG. 13A shows a planar structure, and FIG.13B shows a cross-sectional structure.

As shown in FIGS. 13A and 13B, when a semiconductor wafer 10 is cleaved,cleavage cracks, steps, and the like are generated intensively at theend portion 32 b of each groove 32. In this embodiment, cleavage cracksare also generated intensively at the stepped portion 35 formed betweenthe groove 32 and the ridge stripe portion 23 a. As a result, anaccurate cleavage line is obtained in the region between the steppedportions 35, 35, and generation of cleavage cracks can be suppressed inthe region including the ridge stripe portion 23 a.

In this embodiment, the stepped portion 35 is a mesa-shaped steppedportion extending in the direction parallel to the extending directionof the ridge stripe portion 23 a. However, the stepped portion 35 needonly be formed as a step of several micrometers between the groove 32and the ridge stripe portion 23 a. As shown in FIGS. 14A and 14B, thestepped portion 35 may be formed by forming between the groove 32 andthe ridge stripe portion 23 a a groove extending in the directionparallel to the extending direction of the ridge stripe portion 23 a. Inthis case, the grooves 32 and the stepped portions 35 can be formedsimultaneously by etching. Therefore, the number of processes is notincreased, which is economically advantageous. The stepped portion 35may have another structure as long as a step of several micrometers canbe formed between the groove 32 and the ridge stripe portion 23 a in thedirection parallel to the extending direction of the ridge stripeportion 23 a.

Third Embodiment

Hereinafter, a third embodiment of the invention will be described withreference to the drawings. FIGS. 15A and 15B show a structure of aportion between grooves 32 of a semiconductor laser device of the thirdembodiment. FIG. 15A shows a planar structure and FIG. 15B shows across-sectional structure. In FIGS. 15A and 15B, the same elements asthose of FIGS. 3A and 3B are denoted with the same reference numeralsand characters, and description thereof will be omitted.

As shown in FIGS. 15A and 15B, each groove 32 of the semiconductor laserdevice of this embodiment is formed by a shallow groove 32A and a deepgroove 32B. The shallow groove 32A is formed by dry etching, and thedeep groove 32B is formed by scribing a central part of the shallowgroove 32A.

When a groove is formed by scribing, the depth of the groove can beeasily increased. With scribing, however, grooves cannot be formed witha uniform shape. Therefore, cleavage cracks and the like are likely tobe produced, and a cleavage line cannot be accurately controlled. On theother hand, when a groove is formed by etching, it is difficult to forma deep groove. However, when the groove is too shallow, it is difficultto form an accurate cleavage line between the ends of the grooves.Moreover, the cleavage line may be displaced from the grooves, wherebythe grooves may lose their function as a cleavage guide groove.

Since accuracy of the cleavage line is not required in the central partof the groove 32, the central part of the groove 32 is formed as a deepgroove 32B formed by scribing. Since the end of the groove 32 needs tohave an accurate shape, the end of the groove 32 is formed as a shallowgroove 32A formed by etching. In this way, even when the groove 32A isshallow, an accurate cleavage line can be realized in the portionbetween the grooves 32.

The deep groove 32B can be formed by first forming the shallow groove32A by dry etching and then scribing the central part of the shallowgroove 32A with a diamond needle. Laser beams, electron beams, or thelike may be used instead of a diamond needle. By using an appropriatespot size and power of laser beams, electron beams, or the like, deepguide grooves can be formed as in the case of scribing with a diamondneedle. Scribing with laser beams or electron beams can improve the scanspeed as compared to scribing with a diamond needle. Therefore,processing time can be significantly reduced.

Fourth Embodiment

Hereinafter, a fourth embodiment of the invention will be described withreference to the drawings. FIGS. 16A and 16B show a structure of aportion between grooves 32 of a semiconductor laser device according tothe fourth embodiment. FIG. 16A shows a planar structure, and FIG. 16Bshows a cross-sectional structure. In FIGS. 16A and 16B, the sameelements as those in FIGS. 3A and 3B are denoted with the same referencenumerals and characters, and description thereof will be omitted.

As shown in FIGS. 16A and 16B, each groove 32 of the semiconductor laserdevice of this embodiment has a width that varies in two stages. Morespecifically, each groove 32 is formed by a first region 32C having alarger width and a second region 32D formed on both sides of the firstregion 32C and having a smaller width than that of the first region 32C.

As described before, the functioning ratio of a cleavage guide decreasesas the width of the groove 32 decreases. However, this happens for thefollowing reason: with a small width w, a cleavage line 51 cannot bereturned to the inside of the groove 32 once the cleavage line 51 isdisplaced. As a result, almost all of resonators arranged in a line havedefective cleavage. When only the examples in which the cleavage line 51could be kept within the groove 32 are compared, it is found that higheraccuracy of the cleavage line 51 can be obtained from a groove 32 havinga smaller width. In this embodiment, therefore, each groove 32 is formedfrom a first region having a large width w and a second region having asmall width w, whereby accuracy of the cleavage line 51 between therespective end portions of the grooves 32 is improved. Moreover, evenwhen the cleavage line 51 is displaced, the cleavage line 51 can bereturned to the inside of the groove 32. The first region 32C has awidth w₁ in the range of 20 μm to 50 μm, and the second region 32D has awidth w₂ in the range of 2 μm and 10 μm.

As shown in FIGS. 16A and 16B, it is preferable that each groove 32 havea portion with a gradually reduced width w between the first region 32Cand the second region 32D. In this case, the planar shape of each groove32 has the first region 32C as a protruding portion having a planarisosceles trapezoid shape and protruding in both directions parallel tothe extending direction of the ridge stripe portion 23 a. Like the angleθ of the tip of the groove 32, an inclination angle of a portion of thefirst region 32C which has a gradually reduced width w, that is, aninclination angle of a portion corresponding to the oblique side of theisosceles trapezoid, is preferably in the range of 10 degrees and 40degrees. This increases probability that the direction of the cleavageline 51 displaced within the groove 32 is corrected and guided to thetip of the groove 32. It should be noted that the inclination angle doesnot need to be the same as the angle θ at the end portion of the groove32.

A ridge-type semiconductor laser device is described in the firstthrough third embodiments. However, the invention can be applied to anelectrode stripe type semiconductor laser device, a buried stripe typesemiconductor laser device, and the like. In the above embodiments, thegrooves 32 are formed from the side of the nitride semiconductormulti-layer 12. However, the same effects can be obtained even when thegrooves 32 are formed from the side of the substrate 11.

As has been described above, the semiconductor laser device and themanufacturing method thereof according to the invention can implement asemiconductor laser device formed from a semiconductor material of ahexagonal system such as a nitride semiconductor and having astructurally stable cleavage facet. The semiconductor laser device andthe manufacturing method thereof according to the invention areespecially useful as a semiconductor laser having a resonator end facetformed by cleavage and a manufacturing method thereof.

1-11. (canceled)
 12. A method for manufacturing a semiconductor laserdevice, comprising the steps of: (a) forming a semiconductor wafer thathas a plurality of stripe-shaped wave guide portions extending in onedirection at intervals by first forming on a substrate a semiconductormulti-layer including an n-type clad layer, an active layer, and ap-type clad layer and then selectively etching the p-type clad layer;(b) selectively etching the semiconductor wafer having the plurality ofwave guide portions to form a plurality of grooves arranged in a line ina region except for the wave guide portions in a direction crossing anextending direction of the wave guide portions; and (c) by using theplurality of grooves arranged in a line as a cleavage guide, forming acleavage facet exposing the wave guide portions along the cleavageguide, wherein each groove has an end portion at at least one of its twoends located in a direction crossing an extending direction of the waveguide portions, the end portion having a V shape when viewed twodimensionally, and an angle between two sides surrounding the endportion is in a range of about 20 degrees to about 80 degrees, and anangle between an extending direction of at least one of the two sidessurrounding the end portion and a direction in which the cleavage facetis formed is in a range of about 10 degrees to about 40 degrees.
 13. Themethod for manufacturing a semiconductor laser device according to claim12, wherein each groove has the end portion at both of its two endslocated in the direction crossing the extending direction of the waveguide portions.
 14. The method for manufacturing a semiconductor laserdevice according to claim 12, wherein a planar shape of each groove hasa protruding portion having a planar isosceles trapezoid shape andprotruding in both directions parallel to the extending direction of thewave guide portions, the protruding portion of each groove has a widthof about 20 μm to about 50 μm in the direction parallel to the extendingdirection of the wave guide portions, a remaining portion of eachgroove, a portion excluding the protruding portion, has a width of about2 μm to about 10 μm in the direction parallel to the extending directionof the wave guide portions, and an angle between an extending directionof an oblique side of the protruding portion and a direction in whichthe wave guide portions are formed is in a range of about 10 degrees andabout 40 degrees.
 15. The method for manufacturing a semiconductor laserdevice according to claim 12, further comprising, after the step (b) andbefore the step (c), the step of: (d) scribing at least a portionexcluding the end portion in each groove to make the portion excludingthe end portion deeper than the end portion.
 16. The method formanufacturing a semiconductor laser device according to claim 15,wherein the scribing is conducted with a diamond needle.
 17. The methodfor manufacturing a semiconductor laser device according to claim 15,wherein the scribing is conducted using laser beams or electron beams.18. The method for manufacturing a semiconductor laser device accordingto claim 12, wherein the step (a) includes the step of forming amesa-shaped stepped portion by selectively etching a portion on bothsides of each wave guide portion in the semiconductor multi-layer, andin the step (b), each of the grooves is formed in a region other thanthe stepped portion.
 19. The method for manufacturing a semiconductorlaser device according to claim 12, wherein the step (b) includes thestep of forming a additional groove in a region between each wave guideportion and each groove in the semiconductor wafer so that theadditional groove extends in a direction parallel to the extendingdirection of the wave guide portions.
 20. The method for manufacturing asemiconductor laser device according to claim 12, wherein an anglebetween an extending direction of one of two sides surrounding the endportion and a direction in which the cleavage facet is formed is in arange of about 10 degrees to about 40 degrees, and an extendingdirection of another one of the two sides surrounding the end portionmatches the direction in which the cleavage facet is formed.
 21. Themethod for manufacturing a semiconductor laser device according to claim12, wherein each groove is formed from a side of the semiconductormulti-layer in the wafer.
 22. The method for manufacturing asemiconductor laser device according to claim 12, wherein each groove isformed from a side opposite to the semiconductor multi-layer in thesubstrate of the wafer.